Devices of this type are known in the state of the art. Thus, Document FR 2 640 589 describes a metering pump for dispensing small-volume drops, the pump comprising a pump body having an open end communicating with a container of the substance to be dispensed, and an end provided with an end wall pierced by a central orifice. A piston secured to a push rod slides in sealed manner inside the pump body, while the push rod slides through the central orifice in the end wall of the pump body. Said push rod includes a central channel opening out axially to the outside of the pump, and radially in the vicinity of the piston into a pump chamber which is delimited by the piston and the pump body, said pump chamber extending between the piston and the end wall of the pump body. The outside end of the central channel in the rod is provided with an outlet valve which may be in the form of two hemispheres that are connected together by a resilient spacer. In addition, a return spring applies resilient thrust to the push rod, thereby urging the piston towards the end wall of the pump body. When a user presses on the push rod, generally via a pusher, the piston is pushed into the container of substance until it leaves the pump body: so long as the piston has not left the pump body, this movement sets up suction in the pump chamber because the outlet valve remains closed; when the piston leaves the pump body, a measured quantity of substance is sucked into the pump chamber. When the user releases the push rod, the piston is returned towards the end wall of the pump by the return spring, and as a result the substance contained in the pump chamber is compressed and ejected via the central channel of the push rod and via the outlet valve which opens under the effect of applied pressure.
Such metering pumps nevertheless suffer from the drawback that the outlet valve is a very small part which is quite difficult to make and to assemble, thereby significantly increasing the cost of the pump. Similarly, the fact that the push rod includes an axial channel and a radial channel means that it must be molded in a special mold including a sliding pin. Such molds are expensive and relatively fragile and thus have an unfavorable influence on the cost of the pump. Since such pumps are designed to be discarded once their container of substance has been emptied, it is appropriate to minimize the cost thereof.
An object of the present invention is to provide a device for dispensing drops of small volume while avoiding the above-mentioned drawbacks.